(a) Technical Field
The present invention relates to a pressure vessel for storing high-pressure gas, more particularly, to a structure for ensuring gastightness of a nozzle unit vulnerable to a gas leak in a pressure vessel for storing high-pressure gas, and a pressure vessel including the nozzle unit.
(b) Description of the Related Art
A gas storage vessel is needed to store various types of gases such as hydrogen, nitrogen, and natural gas and discharge the stored gas as necessary. In particular, gas needs to be stored in a high-pressure state because the storage density of gas in the vessel is low, and under this high pressure environment, it is essential to use a pressure vessel.
For example, in the case of alternative fuel gas vehicles (fuel cell vehicles or compressed natural gas vehicles), structures of storage systems vary in accordance with a method of storing fuel gas, and recently, a method which stores gas in the form of compressed gas in consideration of costs, weight, and simplicity of the storage system, has been considered. However, because energy storage density of gaseous fuel is low, the storage amount or storage pressure needs to be increased to ensure a longer traveling distance. In the case of a vehicle, a space for mounting a gas storage system is limited, and there is a limitation in increasing a size of a storage tank. As a result, it is critically important to tank technology to safely store higher pressure gas.
In the case of a composite tank among fuel gas storage tanks, an outer cover is reinforced by a fiber reinforced composite material with high specific strength and specific stiffness, and a liner for maintaining gastightness is inserted into the composite tank in order to withstand internal pressure caused by compressed gas. Based on a material of the liner, the shape of the fuel gas storage tank is classified into a type 3 tank in which a liner made of a metallic material such as aluminum is inserted, and a type 4 tank in which a high-density polymer liner is inserted. The type 3 tank has relatively high stability but is expensive and has a low anti-fatigue property. In contrast, the type 4 tank is inexpensive and has better anti-fatigue property in comparison with the type 3 tank, but could have a safety problem such as a leakage of hydrogen and deterioration of anti-permeation performance. In particular, because of a difference in material between a metallic nozzle and a plastic body which are applied to mount an external valve, ensuring gastightness (soundness) at a coupling portion is critical.
The above information disclosed in this Background section is only for enhancement of understanding the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.